1. Field of the Invention
This invention relates to a pump for a printing machine for supplying ink while a plunger is rotated and reciprocated by a motor in an offset printing machine.
2. Description of the Background Art
There are conventionally many known examples of a pump for an offset printing machine. For example, Japanese Patent No. 286447 (prior art) discloses an ink pump for a printing machine for supplying ink by repeatedly reciprocating a plunger within a cylinder once while the plunger is rotated once by using a variable speed motor.
In the pump for a printing machine of the prior art, as shown in FIG. 7, a cylinder 102 has a suction hole 121 and a discharge hole 122 opened in positions in which a main hole 120 closed on one side thereof is shifted by 180 degrees in phase. This cylinder 102 is fixed to one side of a base 101 through the space of a hollow portion thereof. A plunger 103 is fitted and inserted into the main hole 120 of the cylinder 102 on the other side thereof so as to be rotated and reciprocated. The cylinder 102 is closed by the plunger 103. One portion of a fitting circumferential face of the plunger 103 to the cylinder 102 is notched until its end tip and one end of the plunger 103 is projected from the other side of the main hole 120 to the hollow portion of the base 101 such that either the suction hole 121 or the discharge hole 122 can be communicated with the main hole 120 by rotating the plunger 103.
A variable speed motor 104 is attached to the base 101 in accordance with the plunger 103. An output shaft 140 of the variable speed motor 104 is projected to the hollow portion of the base 101. A rotating central line of the output shaft 140 is set to cross a rotating central line of the plunger 103 by a predetermined angle. Further, an arm 160 is attached to the output shaft 140 so as to project to the hollow portion. A spherical bearing 162 arranged at the other end of the arm 160 and an end portion side of the plunger 103 are connected to each other by a connection member 161 so that a crossing angle between the rotating central line of the output shaft 140 and an axis of the connection member 161 can be changed.
The crossing angle between the rotating central line of the output shaft 140 and the axis of the connection member 161 becomes maximum at the final stage of a sucking stroke and becomes minimum at the final stage of a discharging stroke at the time of a rotating phase in which the plunger 103 simultaneously closes the suction hole 121 and the discharge hole 122 every half rotating phase of the plunger 103.
FIGS. 8a to 8f are partial sectional perspective explanatory views showing an operating mode of the plunger 103 of the prior art, showing an operating mode where the plunger 103 is reciprocated once while the plunger 103 is fitted into the main hole 120 of the cylinder 102 and is rotated once in the direction of an arrow X.
FIG. 8a shows a terminating state of the sucking stroke in which the plunger 103 is located at an upper dead point and closes the suction hole 121 and the discharge hole 122.
FIGS. 8b and 8c show states of the discharging stroke. In these states, while the suction hole 121 is closed, the plunger 103 is moved in an inserting direction of the main hole 120 while the plunger 103 is rotated in the direction of the arrow X. Then, ink is discharged from the discharge hole 122.
FIG. 8d shows a terminating state of the discharging stroke in which the plunger 103 is located at a lower dead point and closes the suction hole 121 and the discharge hole 122.
FIGS. 8e and 8f show states of the sucking stroke. In these states, while the discharge hole 122 is closed, the plunger 103 is moved in a direction pulled out of the main hole 120 while the plunger 103 is rotated in the direction of the arrow X. The ink is then sucked from the suction hole 121.
In the pump P of the prior art, ink piping is connected between a fluid passage on an ink discharging side and an ink rail to discharge the ink sucked from an external ink tank.
When the variable speed motor 104 for operating the plunger 103 is a stepping motor 104 shown in an embodiment mode of the prior art, rotation of this stepping motor is controlled by a pulse signal. When it is not necessary to discharge the ink, or when the stepping motor is intermittently driven to adjust a discharging amount of the ink, the rotation of a rotor of the stepping motor 104 corresponding to the plunger 103 is stopped in accordance with necessity. Further, an exciting current flows through the stepping motor to self-hold a stopping position of this stepping motor 104, or the electric current flowing through the stepping motor 104 corresponding to the plunger 103 is interrupted in accordance with necessity so that an unmagnetizing state is set. Thus, the operation of the plunger 103 is ceased or is temporarily stopped.
The above prior art has several problems to be solved. For example, in the pump P of the prior art, the internal pressure of the ink pipe on the discharging side is increased by a discharging pressure of the ink at the discharging stroke of the ink so that force for pushing back the plunger 103 is caused. Further, at the discharging stroke of the ink, the crossing angle between the rotating central line of the output shaft 140 and the axis of the connection member 161 is gradually changed from a maximum angle to a minimum angle. Accordingly, the force for pushing back the plunger 103 is applied such that the arm 160 is angularly displaced in a reverse direction through the connection member 161 and the spherical bearing 162. Thus, the output shaft 140 begins to be angularly displaced in the reverse direction.
In rotating control using the stepping motor 104, a method for performing a magnetizing operation by flowing an electric current through winding of the stepping motor 104 is adopted to give self holding force to the output shaft 140 such that the output shaft 140 is not rotated by an external force during stoppage of the stepping motor. The stepping motor 104 is heated by this magnetizing electric current. There is a case in which the surface temperature of the stepping motor 104 is increased to 60 degrees centigrade or more in accordance with an operating condition of the pump P.
When the printing machine is operated at a relatively low speed, or the number of image lines of a printing plate is small, an ink supplying amount per unit time is small so that a stopping time of the pump P is lengthened. Therefore, the exciting current flows through the stepping motor during the stoppage of the pump P so that the stepping motor is heated. Accordingly, there is a case in which the stepping motor abnormally rises in temperature.
The temperature due to these heatings is transmitted to the base 101 and the cylinder 102 is heated so that the temperature of the ink rises and ink viscosity is reduced and the ink supplying amount becomes unstable and has a bad influence on printing quality. Further, when the electric current flowing through the stepping motor 104 is interrupted at the time of a pump stopping state during the operation of the printing machine to avoid this heating and no magnetizing operation is performed to restrain the heating, the plunger 103 is pushed back by the internal pressure of the ink piping on the discharging side caused by the ink discharging stroke. Displacement of the plunger 103 is transmitted to the arm 160 through the connection member 161 and the spherical bearing 162 so that the output shaft 140 is angularly displaced in a reverse direction. As a result, pulse signals are again transmitted by the next control amount from an unillustrated control means with a returning position of the plunger 103 as a starting point so that the stepping motor 104 is angularly displaced. Accordingly, the discharging amount of the ink is reduced by the returning amount of the plunger 103.
FIG. 9 is a graph of an arm rotating curve showing the relation of an arm rotating angle with respect to an arm rotating period in the prior art and the internal pressure of a fluid passage on a side of the discharge hole, and an internal pressure curve of the ink piping on the discharging side. When there is a resistance object such as an ink rail, etc. at a terminal of the ink piping on the discharging side of the pump of the prior art, the relation of the discharging side pressure of the pump P and the arm rotating period is explained by this graph.
An arm rotating curve (A) shown by a broken line shows a case in which there is no loss of the angular displacement of the arm in a reverse direction at the discharging stroke and rotating stoppage of the arm is ideally repeated. An arm rotating curve (B) shown by a solid line shows a case in which the ink is discharged while the angular displacement of the arm is repeated in the reverse direction by the internal pressure every time the arm is operated at the discharging stroke. The arm rotating curves (A) and (B) also show a relation for controlling the operation of the pump such that a group of pulse signals required to angularly displace the arm by 45 degrees are given to the stepping motor so as to displace the arm and the stepping motor is then stopped by the number of pulses corresponding to this displacement. When a group of pulse signals for continuously angularly displacing the arm by 45 degrees are given to the stepping motor four times, the stepping motor is angularly displaced by 180 degrees and the arm is angularly displaced by 180 degrees so that the sucking stroke is terminated. Thereafter, when a group of pulse signals are similarly given four times, the arm is angularly displaced by the next 180 degrees without any loss with respect to the arm rotating curve (A) and the discharging stroke is terminated.
As can be seen from FIG. 9, when the stepping motor is rotated 360 degrees, one rotating period of the arm is terminated. A rightward rising gradient portion at the sucking stroke of each of the arm rotating curves (A) and (B) shows that the arm is being normally angularly displaced in a predetermined operating direction. Further, a portion of each of the arm rotating curves (A) and (B) parallel to an axis of abscissa shows that the pump P is being stopped. Namely, when the pump P, is stopped, the arm rotating curve (B) must be originally parallel to the axis of absissa, but this curve portion shows a rightward falling gradient at the discharging stroke of the prior art. This shows that the arm is returned and is angularly displaced in the reverse direction. Namely, the output shaft of the stepping motor is angularly displaced in the reverse direction and a substantial angular displacing amount of the arm is reduced. Accordingly, the rotating period of the arm rotated once is lengthened so that the relation of the arm and the control system transmitting rotating commands to the pump is unbalanced and a suitable amount of ink is not supplied and the ink is insufficient. Thus, problems exist in that the ink amount required on a printing paper face is not supplied to the printing face, and ink density on the printing paper face is reduced, causing printing quality to be reduced.
To simultaneously solve the above problems in the prior art, an object of this invention is to provide a pump for a printing machine in which a plunger temporarily stopped at a discharging stroke during an operation of the pump intermittently separately operated by a motor is not retreated and angularly displaced in a direction reverse to a predetermined operating direction so that a required ink amount can be supplied onto a printing paper face.
To solve the above problems, this invention provides a pump for a printing machine for sucking and discharging ink by repeatedly reciprocating a plunger operated by a motor once while the plunger is rotated once within a main hole of a cylinder, the pump comprising:
a base;
the cylinder which is attached to the base and has the main hole closed on one side thereof and also has a suction hole and a discharge hole opened in positions different from each other in phase on an inner circumferential face of the main hole;
the plunger which is fitted onto an opening side of the main hole of the cylinder so as to be axially moved and rotated from an end tip of the main hole and simultaneously close the suction hole and the discharge hole of the cylinder in a certain rotating phase and also close one of the suction hole and the discharge hole in a different rotating phase;
the motor attached to the base such that a rotating central line of a rotating shaft crosses that of the plunger at a predetermined crossing angle;
a transmission mechanism which is constructed by an arm fixed to the output shaft of the motor and approximately projected in parallel with the rotating central line of the output shaft of the motor, and is also constructed by a connection member slidably attached to an inner ring hole of a spherical bearing fixed to the arm and fixed to a rear end side of the plunger and connecting the arm and the plunger to each other; and
retrogression preventing means for arranging the plunger temporarily stopped at a discharging stroke during an operation of the pump intermittently operated by the motor such that the plunger is not retreated and not angularly displaced in a direction reverse to a predetermined operating direction.
This invention also provides a pump for a printing machine for sucking and discharging ink by repeatedly reciprocating a plunger operated by a motor once while the plunger is rotated once within a main hole, the pump comprising:
a cylinder-base which has the main hole closed on one side thereof and also has a suction hole and a discharge hole opened in positions different from each other in phase on an inner circumferential face of the main hole;
the plunger which is fitted onto an opening side of the main hole so as to be axially moved and rotated from an end tip of the main hole and simultaneously close the suction hole and the discharge hole in a certain rotating phase and also close one of the suction hole and the discharge hole in a different rotating phase;
the motor attached to the cylinder-base such that a rotating central line of a rotating shaft crosses that of the plunger at a predetermined crossing angle;
a transmission mechanism which is constructed by an arm fixed to the output shaft of the motor and approximately projected in parallel with the rotating central line of the output shaft of the motor, and is also constructed by a connection member slidably attached to an inner ring hole of a spherical bearing fixed to the arm and fixed to a rear end side of the plunger and connecting the arm and the plunger to each other; and
retrogression preventing means for arranging the plunger temporarily stopped at a discharging stroke during an operation of the pump intermittently operated by the motor such that the plunger is not retreated and not angularly displaced in a direction reverse to a predetermined operating direction.
The above retrogression preventing means is arranged in at least one rotating member of the plunger having a rotating action, the arm and the output shaft of the motor.